The invention relates to a method and to a packet radio system implementing the method with which a mobile phone network according to the GPRS system is able to optimize radio channel access delay.
A packet radio system refers to a radio system employing the packet switching technology that is known from fixed networks. Packet switching is a method where a connection is set up between users by transmitting data in packets which contain address and control information. Several connections can utilize simultaneously the same transmission link. The use of packet switched radio systems has been under special research since the packet switching method is very well suited to data transmission where the data to be transmitted is generated in bursts. There is thus no need to reserve a transmission link for the entire duration of transmission but only for the time when packets are transmitted. This saves costs and capacity considerably during both the set-up and use of the network.
Packet switched radio networks are presently of particular interest in the further development of the GSM system, in which case they are referred. to as General Packet Radio Service (GPRS). For example GSM specification 03.64 of the ETSI describes a radio interface between a network element and a subscriber terminal in the GPRS.
Unlike in a conventional GSM system, in the GPRS system a subscriber terminal is able to listen to more than one paging subchannel in a manner defined in the GPRS standard, and different subscriber terminals can determine themselves how often they want to listen to paging subchannels.
Therefore the mobile network is able to optimize the use of the paging subchannels such that the average radio channel access delay to a subscriber terminal is reduced.
However, a problem of the prior art arrangements is, for example, that radio resources are out of use. This problem only arises if the logic unit which makes a decision concerning the allocation of radio resources in the GPRS, i.e. a packet control unit PCU, does not also attend to the timing of the control channel, which can be either a packet common control channel
PCCCH or a common control channel CCCH. Problems occur, for example, if the radio resources are allocated in the base station controller but the timing of the control channel takes place at the base station.
Another problem with the prior art arrangement is the increase in the power consumption. The GPRS determines a so-called extended paging procedure whereby it is possible to reduce the average channel access delay. A drawback of this method is that it increases the power consumption of the subscriber terminals within the cell area since the terminals must listen to the paging subchannels more often.
An objective of the present invention is to develop a method of reducing radio channel access delay in a packet radio system, and a packet radio system, such that the aforementioned problems can be solved. This is achieved with a method described below, The invention relates to a method of reducing radio channel access delay in a packet radio system, which system comprises a network element and at least one subscriber terminal, which network element transmits channel allocation messages to the subscriber terminals, which channel allocation messages are transmitted by means of paging subchannels, and which subscriber terminals listen to one or several paging subchannels. In the method the channel allocation messages to be transmitted to the subscriber terminals are organized such that the cumulative total delay of all the channel allocation messages is minimized by optimizing the use of the paging subchannels.
The invention also relates to a packet radio system comprising a network element and at least one subscriber terminal, wherein the network element is arranged to transmit channel allocation messages to the subscriber terminals by means of a number of paging subchannels, and which subscriber terminals are arranged to listen to one or several paging subchannels. The packet radio system is arranged to organize the channel allocation messages to be transmitted to the subscriber terminals such that the cumulative total delay of all the channel allocation messages is minimized by optimizing the use of the paging subchannels. The preferred embodiments of the invention are disclosed in the dependent claims.
In the invention, channel allocation messages transmitted in a GPRS mobile network in accordance with discontinuous reception (DRX) are preferably organized such that they can be transmitted over the radio path as rapidly as possible.
The method and the system according to the invention provide several advantages. The method according to the invention reduces the channel access delay of a subscriber terminal and shortens the time when the radio resources are unnecessarily allocated. However, the method according to the invention does not increase the power consumption of the subscriber terminals within the cell area. Messages intended for subscribers using the DRX parameters are timed such that the cumulative total delay of all the messages is minimized. Therefore, due to the method according to the invention the use of the paging subchannels can be made considerably more effective, which results in a shorter average channel access delay for the subscriber terminals. The subscriber terminals are thus served more rapidly and the degree of use of the radio resources in the GPRS mobile network is improved.